In my previous application Ser. No. 954,689, now U.S. Pat. No. 4,233,029, I describe a liquid transport device formed by opposed surfaces spaced apart a distance effective to provide, through a zone of intended transport, capillary flow of liquid. Once the liquid is introduced into such a device, it continues to flow between the surfaces until either the volume of liquid is exhausted or an edge of the zones is encountered. There is no capability for temporarily stopping liquid flow within a portion of the device, and thereafter resuming the flow, other than by adding more liquid to an exhausted supply of liquid. Temporary stoppage and resumption of flow would be particularly useful for sequential reactions conducted on a constant volume of liquid, such as in an assay of the liquid using sequential reagents separated within the device. The addition of more liquid to cause resumption of flow is not a useful technique when the reaction dictates that the liquid volume or concentration of analyte must remain constant.
Accordingly, what has been desired is a reaction vessel or test device featuring capillary attraction as the means for moving liquid therein, the device being operative to temporarily stop the flow of a given volume of liquid to allow a reaction with a reagent, and thereafter to resume the flow of the liquid for further processing. Such a device would permit immunoassays to be conducted, for example, using labeled antigens or antibodies, and the complementary immunogen as the reagent that reacts (by binding) while the liquid is temporarily stopped. Resumed flow would cause separation of the bound and of the free labeled antigen or antibody into two different zones of the device, permitting accurate detection of the labeled antigen or antibody, and the calculation of the liquid immunogen that is present.